June 6, 2012 -- Children who have multiple CT scans before they reach their mid-teens have an increased risk for
leukemia and brain tumors, a new study shows.

Assuming typical doses of radiation, researchers concluded that having as few as two to three computed tomography (CT) scans of the head before the age of 15 could triple a child's risk for developing a brain tumor, while five to 10 head scans may triple leukemia risk.

CT imaging is increasingly used in the United States and elsewhere to evaluate injuries and illness in children.

'First Direct Evidence of Cancer Link'

In the new study, researchers from Newcastle University in the United Kingdom followed more than 178,000 children who had CT scans from the mid-1980s through 2002 for as long as two decades after exposure.

Studies of atomic bomb survivors in Japan long ago found radiation exposure to be associated with a higher cancer risk in children than adults.

But the new findings provide the first direct evidence of a link between diagnostic CT scans and cancer risk in children, researcher Mark S. Pearce, PhD, of Newcastle University, said in a news conference.

The study was jointly funded by the National Cancer Institute in the U.S. and the Department of Health in the United Kingdom.

"Ours is the first direct study of cancer risk in patients who have undergone a CT," he said.

"We all agree that CT scans are very useful, but they also have about 10 times the radiation of an X-ray," he said. "The increasing use of CT around the world has raised concerns about whether more needs to be done to assess safety."

Risk to Individual Children Very Small

While the study directly links CT imaging with cancer risk later in life, the overall risk to the individual child remains very low.

The researchers estimated that for every 10,000 head CT scans performed on children 10 years old and younger, one case of leukemia and one brain tumor could be expected within a decade of first exposure.

In an editorial published with the study, imaging specialist Andrew J. Einstein, MD, of Columbia University Medical Center in New York, writes that since clinical practice has changed in the past decade to minimize radiation exposure, the finding may overestimate risk for CTs delivered today.

"New CT scanners all now have dose-reduction options, and there is far more awareness among practitioners about the need to justify and optimize CT doses," he writes.

Einstein tells WebMD that parents should not be overly alarmed by the new study, but they should also not be afraid to ask questions if a CT scan is recommended for their child.

"We certainly don't want parents to avoid scans when they are necessary," he says. "If a child has abdominal pain and there is a concern about appendicitis or if there is head trauma and there is concern about bleeding in the brain, a CT scan can save a child's life."

Still Room for Improvement, Expert Says

He says while efforts to increase awareness about unnecessary or inappropriate pediatric CT scans have had an impact, there is still room for improvement.